Reversible fluid power transfer apparatus

ABSTRACT

In a reversible fluid power transfer package, sensing means detect which of two mechanically interconnected fluid pressure translating devices is required to operate as a pump and which is required to operate as the motor. In response to a signal from the sensing means, dual-functioning check valve-flow limiter components associated with each device are ported according to the required mode of function of the respective device, so that whichever device is to operate as the motor is automatically provided with a flow limiter valve, and whichever device is to operate as the pump is automatically coupled to a check valve on its outlet side. The check valve may incorporate variable bypass features.

United States Patent Coakley 1451 Sept. 19, 1972 [541 REVERSIBLE FLUIDPOWER TRANSFER APPARATUS [72] Inventor: James L. Coakley, Camarillo,Calif.

[73] Assignee: Abex Corporation, New York, NY.

[22] Filed: Nov. 19, 1970 [21] App1.No.: 91,114

3,581,497 6/1971 Krumholz .Q. ..60/53R Primary Examiner-Edgar-W.Geoghegan Assistan! Examiner-L. J. Payne Attorney-Wood, Herron & Evans57 ABSTRACT In a reversible fluid power transfer package, sensing meansdetect which of two mechanically interconnected fluid pressuretranslating devices is required to operate as a pump and which isrequired to operate as the motor. In response to a signal from thesensing means, dual-functioning check valve-flow limiter componentsassociated with each device are ported according to the required mode offunction of the respective device, so that whichever device is tooperate as the motor is automatically provided with a flow limitervalve, and whichever device is to operate as the pump is automaticallycoupled to a check valve on its outlet side. The check valve mayincorporate variable bypass features.

11 Claims, 4 Drawing Figures PATENTED SEP 19 1972 3'69 1, 767

sum 1 BF 2 PATENTEDSEP 19 1972 3.691. 76 7 sumanFz W 5 I mfg 70FREVERSIBLE FLUID POWER TRANSFER APPARATUS This invention broadlyconcerns the transfer of power from a fluid motor operating in one fluidsystem, to a pump operating in a second fluid system. Mechanism of thistype is referred to hereinafter as fluid power transfer apparatus, or asa transfer package.

Such apparatus is utilized to enable one system to drive or providepressure fluid in the second system, as for example where a primarysource of power in the second system fails or is not operating. Eachsystem may and usually does have its own main pump for developingpressure, and the power transfer package is used to drive a secondary orauxiliary pump if the main pump is disabled or is not operating.

Multi-engine aircraft commonly have a plurality of fluid systems. Theseare coupled through a transfer package to provide redundancy so that ifone system fails, another can be used to operate the pressure operateddevices of the aircraft. Thus, if, for example, the main pump shaft ofone fluid system were sheared, the transfer package will deliver torquefrom a motor in a system which remains operating, to an auxiliary pumpin the system in which the main pump is inoperative. Such systems arebecoming common, for example, to operate aircraft landing gear andaerodynamic control surfaces.

Transfer packages are also utilized in aircraft to facilitate groundtesting of the various fluid pressure systems of the aircraft, withoutstarting the engines. An electric motor is energized to drive the mainpump in one system and power from that system can be transferred througha transfer package to the other systems, so that those systems can betested without starting the engines which drive their main pumps, andwithout including separate electric motors in each system for checkouttesting.

It is often desirable to provide means for limiting the flow of fluidthrough the motor of a transfer package. The flow limiting means preventoverspeeding of the motor, such as might occur for example in the eventof a line break in the driven system which would depressurize the pump.That pump would then provide no resistance to motor operation, and themotor would overspeed and possibly be damaged. The flow limiting meansis also useful to limit the amount of power drawn from the motor, toprevent improper operation of the system in which it is installed.

It is also desirable that the pump in a transfer package be connected tothe load system through a check valve on its output side, and that ableed or bypass to tank be incorporated between the pump and checkvalve, so that some fluid can be spilled to tank if the load demand forflow is low. This prevents erratic operation at low demand flow, atwhich the pump otherwise might tend to stall the motor. As a furtherrefinement it is also desirable that the bypass means be variable ratherthan fixed, so that the output flow delivered by the transfer pump issplit or divided between the load system and the reservoir in accordancewith the demand flow to the load. In this regard, my copending U.S. Pat.application Ser. No. 83,330 filed Oct. 23, 1970, discloses a variablebypass for a transfer package whereby the bypass flow can beproportionately and progressively reduced as the demand flow increases,and vice versa.

Thus, the transfer motor should have flow limiting means associated withit, and the transfer pump should have a check valve and a bypass,preferably a variable bypass combined with the check valve associatedwith it. In some instances it is also desirable to have reversibility ofoperation, that is, reversibility of the direction of power transfer sothat the first system can deliver power to the second if necessary, andso that the second can deliver power to the first if necessary. Suchreversibility demands that the fluid pressure translating device in eachsystem must be capable of operating, as conditions warrant, as a motoror as a pump. Where the package is reversible, each fluid pressuretranslating device should be connected to a flow limiting valve when thedevice is operated as a motor, but it should be connected to a checkvalve or variable bypass check valve when it is operated as a pump.

So far as I am aware there is presently available no control for atransfer package which permits reversibility of operation such that thetransfer package may be operated in either direction, and will, ineither direction, have flow limiting means for the motor and a checkvalve or a variable bypass check valve for the pump. It is a primaryadvantage of this invention that it provides such a control.

It is another advantage of the invention that such control capability isprovided with a minimum of components and weight, bearing in mind thatweight of a transfer package is an especially important factor where thepackage is to be used in aircraft.

It is a further advantage of the invention that means are provided whichautomatically sense or detect which of the systems is the output systemand which is the input system, and flow limiting means is automaticallyprovided for the output system and check valve means for the inputsystem.

It is a further advantage of the invention that the sensing meansautomatically reverse the controls, including the flow limiting andcheck valve functions, when the direction of power transfer is reversed.

According to the preferred embodiment of the invention, sensing meansresponds to comparative pressures in the two fluid systems served by thepair of translating devices. Corresponding pressure signals are appliedto two mode determining components with each of which there isassociated a combination or dual acting check valve and flow limiter.Depending upon its porting as established by the mode component, each ofthe dual functioning components can operate either as a flow limiter forthe respective device when the latter is operating as a motor, or as acheck valve when the respective device is operating as a pump. The modecomponent switches the porting of the dual functioning check valve-flowlimiter according to the operation of the associated fluid pressuretranslating device as a motor or as a pump.

Those skilled in the art will recognize that the functions of flowlimiting and check valving are to an extent opposed or inconsistent withone another. Thus, a flow limiter is biased open when a control chamberpressure is equal to the system pressure; conversely, a check valve isbiased shut when the control chamber pressure is equal to the systempressure. Ideally the flow limiter should permit large flow, up to somelimiting value, but the check valve must block flow under the samerelative pressure conditions. These inconsistent functions thereforepresent difficulty if a single component is to be used alternately as acheck valve and as a flow limiter. This invention provides structurewherein both functions are combined in a single dual functioningcomponent which, depending upon porting, does act as a flow limiter oras a check valve.

Each of these dual functioning components includes a movable valveelement or spool slidable in a bore and which is responsive to pressuresacting on opposite surfaces thereof. One surface is exposed to systempressure, and other or opposed surface portions are acted upon bypressures in primary and secondary control chambers. An orifice in thespool cooperates with a port in the bore to form the throttling valvewhen in operation as a flow limiter, and alternately this valve closesto block reverse flow when in operation as a check valve. In addition,the spool has associated with it a bypass feature, which, when the spoolis in use as a check valve, bypasses theentire pump output to tank ifthe fluid system served by the pump requires no demand fluid. As thedemand flow increases the bypass flow is reduced.

A spring urges the spool toward open position. When in use as a flowlimiter, flow through a restrictor creates a pressure difference whichis reflected in both the primary and secondary control chambers. Thepressures in those chambers are increasingly reduced as flow increases.When the system and control pressures are about equal, the spring holdsthe valve open. Thus a net valve closing pressure force is establishedas the result of the higher system pressure in comparison to the lowerpressure in the two control chambers. This net pressure force eventuallyexceeds the spring force and will close the valve as a limiting flow isapproached.

When the flow limiter-check valve component is to operate as a checkvalve, the primary control chamber is ported to communicate with thepump outlet and the secondary chamber is vented to tank. The springtends to open the valve as. before, but the venting of the secondarychamber introduces a closing pressure force bias, which overcomes thespring opening bias, when system pressure equals the pump outletpressure.

The advantages and details of the invention can best be furtherdescribed by reference to the accompanying drawings, in which:

FIG. I is a schematic view of a portion of two fluid systems coupled bya reversible fluid power transfer package and control in accordance witha preferred embodiment of the invention, and includes longitudinalsectional views of the components of the control;

FIG. 2 is a perspective view of the bypass piston of the flowlimiter-check valve component;

FIG. 3 is a view of the right hand check valve-flow limiter component ofFIG. 1, illustrating the flow through the throttling orifice when thecomponent is functioning as a flow limiter; and FIG. 4 is a view of theleft hand check valve-flow limiter component of FIG. 1, illustrating theorifice as it starts to open in operation as a check valve.

In the preferred embodiment of the invention which is shown in thedrawing for purposes of explanation, two fluid pressure translatingdevices 10, 11 are mechanically interconnected by a shaft 12. Each ofthe devices 10 and 11 can be operated alternately as. a pump or as amotor. When one of the devices is operated as a motor it will transmitmechanical power through shaft 12 to drive the other device as a pump.In the drawing, the package is shown with device 10 operating as a motorand drivingdevice 11 as a pump. Each device 10, 11 may be hydraulic orpneumatic; in the following description it is assumed that both arehydraulic.

Preferably one of the devices 10, II is of variable displacement, sothat its volumetric displacement per unit time can be changed. In FIG. 1device 10 is shown as the variable device, and has displacement changingapparatus operated by a stroking piston or fluid motor 13. Applicationof pressure fluid tostroking piston 13 via line 14 reduces thedisplacement. Device 11 is shown as a fixed capacity device. 7

Each of the pressure translating devices 10 and II may be of generallyconventional type; for example, they may be vane type devices, or axialpiston devices. For that reason their internal constructions are notshown.

Variable device 10 is connected in a fluid system or circuit A, shownonly in part, and on its pressure side has a fluid inlet line 16 whichreceives pressure fluid from the A system in which device 10 -isconnected.

Variable device 10 discharges to an outlet or discharge line 17 insystem A. System A may for example operate landing gear of an aircraft,and includes a primary fluid pump, not shown, which is operated by primemover which may be a main jet engine of the aircraft, or a generatordriven electric motor. That primary pump supplies the pressure fluid toline 16 which operate the pressure translating device 10 as a motor.

Fixed device 11 receives fluid from an inlet line 18, and on itspressure side discharges pressure fluid to an outlet line 19. Under theoperating conditions shown in the illustration, with device 11 operatingin the pump mode, line 18 is a suction line and line 19 is a pressureline. As will be described, the pressure fluid demanded by the work loadis supplied from line 19 to the system B which includes the load. Likesystem A to which variable device 10 is connected, system B includes aprimary pump, not shown, which may also be operated by an electric motoror by an aircraft engine.

Unless or until some reason arises for transferring power from onecircuit to another, the devices 10 and 11 are ordinarily blocked fromtheir respective systems in order to minimize the waste of power throughfriction. For this purpose blocking valves 22 and 23 may be provided.When the valves 22 and 23 are closed, the entire transfer package isbypassed by the fluid flowing in the A and B systems; when the valves 22and 23 are open, devices 10 and 11 are subjected, on their pressuresides, to the pressure of fluid in the respective systems. In the eventof pressure failure in one of the systems A or B, or other event such asground checkout which makes it desirable to transfer power from onesystem to the other, the blocking valves 22 and 23 are opened, eithermanually or electrically, thereby connecting the devices 10 and 11 inthe respective systems, so that power transfer can occur.

In the conditions shown in FIG. 1 it is assumed that power is to betransferred from system A to system B.

Loss of power in the B system may have arisen, for example, by shearingof the shaft of the main pump in that system so that no pressure isdeveloped in line 19. The fluid power transfer package is used todeliver power in the form of mechanical torque through shaft 12 to drivedevice 11 as a pump so that device 11 will supply fluid pressure to line19 to operate the load served by the B system.

The transfer package generally designated by 24 which responds to thereduction or loss of pressure in a system to actuate the packagecontrols by which reversibility is achieved. The device is served bythree components, a pressure sensing shuttle half indicated generally at25 and which is part of the sensing means 24, and controls including amode shuttle designated generally at 26 and a combination or dualfunction flow limiter-check valve component designated generally at 27.The other fluid pressure translating device 11 is served by a pressuresensing shuttle half 250, which is also part of the sensing means 24,and controls including a mode shuttle 26a and a combination or dualfunction flow limitercheck valve 27a. As can be seen from FIG. 1, theshuttle half 25 associated with variable device 10 is similar to theshuttle half 25a associated with fixed device 11, except that shuttlehalf 25 includes additional porting for operating the stroking piston13. The shuttle halves 25 and 25a are isolated fluidically but areinterconnected mechanically by a tie rod 30, so that both halves move orshuttle together.

The mode shuttle 26 for the variable device 10 may if desired beidentical to the mode shuttle 26a for the fixed device, although this isnot essential. Similarly, the combination flow limiter-check valve 27may be and is shown as being similar to the component 27a, although theyalso may differ.

Each component 25, 25a, 26, 26a, 27 and 27a operates in either of twomodes, a motor mode and a pump mode. The components of the respectivepairs always operate in opposite modes; that is, when shuttle half 25 isin the motor mode (as shown) the other component 25a of that pair is inits pump mode, and so on.

By reason of the similarity of the respective components as depicted inthe drawings, the identifying numbers applied to elements associatedwith the variable device 10 are applied, with the suffix a, to thecorresponding elements associated with the fixed device ll; thus device25a corresponds to device 25, etc.

It is the function of the sensing means 24 to detect which system A or Brequires transfer of power to it, and to cause the components associatedwith the device 10 or 11 of the other system to provide the flowlimiting function desired for operation of that device 'as a motor. Itis also the function of the sensing means 24 to cause the componentsassociated with the device which is to be driven as a pump, to providethe check valve and bypass function which are desirable for such pumpoperation. In addition, the shuttle half 25 operates the stroking piston13 of the variable device 10.

The mode shuttles 26 and 26a are responsive to the respective sensingshuttle halves 25 and 25a, and in turn they port the respectivecomponents 27, 27a to operate either as a flow limiter or as a variablebypass check valve. Component 27 is shown in FIGS. 1 and 3 includessensing means in operation as a flow limiter, which limits the rate offlow of fluid in line 16 to device 10 when the latter is operating as amotor. Component 27a is shown in FIGS. 1 and 4 in operation as a checkvalve which divides the output flow from the device 11 between the Bsystem and a fluid reservoir as necessary. The Sensing Means Withrespect to the sensing means 24, its half 25 comprises a movable valveelement or spool 32 which is axially slidable in a bore 33. Spool 32 hasspaced circumferential grooves 34 and 35 which are defined between lands36, 37 and 38. An internal passage 40 in spool 32 provides fluidcommunication between groove 34 and end face 41 of the spool. Face 41 isexposed to fluid pressure in a control chamber 44 in bore 33, pressurein which tends to move the spool leftward.

Another internal passage 42 provides fluid communication between groove35 and the other end' face 43, which is exposed to pressure in a chamber45. The latter chamber is vented, for example to tank, not shown,through the case of the variable displacement device 10. (Where thefluids of the two systems are not to be isolated, venting can be to acommon tank or reservoir.) The tie rod 30 extends from the left face 43of spool 32, and interconnects or couples spool 32 to the spool 32a ofcomponent 25a.

Spool 32 has a central recess or bore 47 adjacent face 41, and adiagonal bore 48 connects bore 47 at all times with a peripheral groove49 formed in bore 33. A bore 51 extends from the end of bore 33, and aboss or raised stop 52 around the entrance to bore 51 limits therightward movement of spool 32.

A dumbbell shaped element 53 having enlarged generally sphericalportions at its ends extends between bores 47 and 51. One spherical endportion forms a sliding fluid seal with bore 47 in spool 32, and theother end forms a sliding fluid seal with bore 51. A central bore 55through element 53 equalizes the pressure in bore 47 with the pressurein bore 51 at all times. Those skilled in the art will understand thatthe purpose of the spherical end portions on element 53 is to avoidconcentricity problems that might arise if a straight cylindrical pistonwere provided and the use of such spherical end portions is a desirablebut not a necessary feature of the invention.

The Mode Shuttle Turning next to the mode shuttle 26, it includes aspool element 56 which is slidable in a bore 57. Opposite ends of thespool are exposed to chambers 58 and 59. Spool 56 has three spaced lands61, 62 and 63, separated by grooves 64 and 65. A stop 66 extends fromland 63 in chamber 58 and limits rightward movement of element 56 to theposition shown in FIG. 1. A biasing spring 69 around stop 66 exerts aleftward biasing force on element 56. Chamber 58, in which spring 69 iscontained, is connected by passage 71 to the case of the variabledisplacement device 10 or to a tank.

The bore 57 in which the mode shuttle spool 56 is situated has a groove72 which, when the spool is in the motor mode as shown, is in fluidcommunication with the groove 65 of spool 56 and through that groovewith a second groove 73 in bore 57. In the pump mode (in which the othermode shuttle spool 56a is shown) groove 72 is in communication with thechamber 58, and is blocked from groove 65. Thus, as mode shuttle spool56 moves, land 63 acts as a valve for groove 72 alternately connectingit to the groove 65, and to the bore portion 58. Groove 73 of bore 57connects spool grooves 64 and 65, bypassing land 62, when component 26is in the motor mode. In the pump mode, land 62 blocks communication ofgroove 73 to spool groove 64, but groove 73 remains in communicationwith spool groove 65 (see mode shuttle 26a). A port 76 in bore 57 isconnected by a line 77, to line 16. In the motor mode, land 61 closesport 76; in the pump mod'e, port 76 is in fluid communication with thegroove 64. Chamber 59 of bore. 57 is at all times connected by a gge 79to bore 51 of the pressure sensing shuttle half The Flow Limiter-CheckValve The flow limiter-check valve 27 is contained within a bore 82 andincludes a movable spool 83 and a bypass valve element 84. Spool 83 isslidable in bore 82; valve element 84 is slidable in a bore 102 in afixed insert 103 in bore 82. A spring 85 between insert 103 and spool 83biases the spool downwardly, toward the position shown in FIG. 1.

Spool 83 contains a stopped bore 86, at the lower end of which anorifice or flow restrictor 87 is formed as a smaller diameter throat orchoke around bore 86. Fluid from system A passes directly throughorifice 87 as it flows toward motor (correspondingly, fluid flows frompump 11 through orifice 87a as it flows to system B, see FIG. 4). A port88 in bore 82, below spool 83, at all times communicates the pressure offluid below orifice 87, through a line 89 and a port 90 into chamber 44of pressure sensing shuttle half 25.

A peripheral groove 92 around spool 83 is connected with bore 86 aboveorifice 87 thereof, by a series of ports 93. Groove 92 is at all timesin communication with a port 95 in bore 82, and port 95 leads throughline 96 to groove 73 of mode shuttle 26.

Radial orifices or ports 98 are formed through the side wall of spool83- and form a throttling or choking valve with a peripheral groove 99in bore'82. Groove 99 is connected tothe inlet side of motor 10(correspondingly, the groove 99a of component 27a is connected to theoutlet line 19 of pump 11).

Optional angulated or diagonal bores 100 extend through the wall ofspool 83 from internal bore 86 thereof, and intersect the outside wallclose to the opening thereto of ports 98. As will be explained, theangulation of these diagonal bores 100 imparts greater stability to theoperation of the flow limiter valve.

The insert 103 within which bypass valve element 84 slides is providedto simplify manufacturing, and does not move within bore 82. Element 84is shown in perspective in FIG. 2. It is generally cylindrical in form,and includes a pair of lands 104, 105 separated by a groove 106. Aplurality of longitudinal or axially extending slots 107 extend part wayalong the longitudinal dimension of land 104 from groove 106. Agenerally hemispherical socket or seat 108 is formed at one end of theelement 84, and this seat receives a spherical ball 109 at one end of aconnecting rod 110 which extends loosely through an axial opening 111 inelement 84. At its lower end, connecting rod 110 has another sphericalball 112 and this ball is seated in a generally hemispherical socket 113formed in the upper end of spool 83. Ball 112 is preferably pinned orswaged in socket 113, so that upward movement of element 84 will movespool 83 upward with it. The ball coupling avoids problems of stickingthat can arise from non-concentricity of the axes of bores 82 and 102,much in the manner of element 53. This is a desirable but not anecessary feature.

A body bore 1 14 is formed above bore 102, to permit upward movement of,the element 84 to the position in which element 84a is shown in FIG. 1.Bore 114 is connected by a line 1 15 to the groove 72 of the modeshuttle 26. Y

A diagonal bore 116 provides fluid communication through insert 103between bore 102 therein and a groove 118 around the external surface ofthe insert. A fluid line 1 17 extends between groove 118 and the inletline 16 of device 10 (correspondingly, line 117a is connected to theoutlet line 19 of device 11'). The chamber 119 in bore 82 which is abovespool 83 is connected at all times by a line 120 with groove 64 of themode shuttle 26. Chamber 119 is a main or primary control chamber forthe operation of spool 83, and bores 102 and 1 14 comprise a secondarycontrol chamber. Operation r The transfer apparatus will transfer powerfrom one system to the other in accordance with the relative pressuresin the two systems. The pressure in system A is reflected at all times(when blocking valve 22 is open) upon surface 41 of pressure sensingshuttle half 25, via port 88, line 89, and port 90. Similarly, thepressure in system B, served by fixed unit 1 1, is reflected on endsurface 41a of pressure sensing shuttle half 25a. The other end faces43, 43a of the respective shuttle halves are exposed to the low pressurein the cases of the variable and fixed units respectively (if fluidisola tion of the two systems is desired). In general the pressures inchambers 45, 45a may be equal and negligible, and the areas of faces 43,43a equal; for purposes of the following discussion it is assumed thatthe forces on the faces 43, 43a are equal and negligible. Thus the onlysignificant forces acting on the pressure sensing shuttles 25, 25a arethe opposed forces resulting from the pressures in lines 79 and 89 onthe right shuttle half 25, and from the pressures in lines 79a and 89aon the left shuttle half 25a. In the condition illustrated in FIG. 1,pressure of fluid in chamber 44 (which is equal to the pressure of fluidin line 89) is applied through bore groove 49, diagonal bore 48 intospool bore 47 and through axial bore 55 into bore 51. Thus essentiallythe same pressure acts across the entire end area of spool 32, and theresulting force holds spool 32, connecting rod 30, and the other spool32a in the position shown in FIG. 1. Fluid in bores 47a and 51a isvented to tank through diagonal bore 48a, groove 49a, spool groove 35a,passage 42a, and chamber 45a which is connected to case. Thus thepressure sensing means is latched in the position shown.

The pressure sensor will remain in this position until the pressure inline 89 (which reflects the pressure in system A) is reduced to a value(normally less than the pressure in system B) determined by the relativeareas of faces 41, 41a and bores 47 and 47a. If the pressure in line 89should drop to that level, then the spools 32,

32a will move rightward and variable unit 10 would be operated as a pumpand fixed unit 11 as the motor. When this motion is accomplished,because of the porting on spools 32 and 32a bore 51a is connected topressure and bore 51 is vented to tank. Thus the spools will remain ineither given position until the pressure drops to the required level forshifting to occur. It will thus be seen that there is a deadband orrange of pressures in which pressure fluctuations do not causeswitching, and this prevents hunting. It will also be appreciated thatthe detection of a malfunction or a need for pressure in one of thesystems such as to require power to be transferred to that system can beaccomplished by other means than the particular pressure sensing meansshown.

By reason of friction and internal loss of power, the capacity ofwhichever device is to act as the pump will usually be less than that ofthe motor driving it. It is to maintain this relation in the reversiblepower transfer package that the displacement of one device is variableand the other is fixed. For the most common case, in which the normaloperating pressure in system A and system B is the same, the maximumdisplacement of the variable device should be greater than thedisplacement of the fixed device; and the minimum displacement of thevariable device should be less than the displacement of the fixeddevice. For example, if the fixed device 11 has a displacement of 10gpm, the variable device could be selected to have a maximumdisplacement of 11 or 12 gpm, and a minimum of'8 or 9 gpm. By operatingthe variable device at its maximum displacement as a motor, itsdisplacement will exceed that of the pump. Similarly, by operating thevariable device at its minimum as a pump, its displacement will then beless than that of the motor driving it. Displacement of variable device10 is increased by release of pressure fluid from behind the strokingpiston 13, through line 14, spool groove 35, passage 42 and chamber 45to the case of the variable unit. When the variable unit is to act as apump, pressure fluid is supplied into line 14 from groove 34, line 40,chamber 44 and line 89 to move the stroking piston to a positioneffecting minimum displacement.

The pressure in bore 51 of the pressure sensing shut tle half 25 isapplied to the mode shuttle 26 through line 79 into chamber 59, where itacts on the end face of spool land 61. The chamber 58 at the other endof spool 56 is vented to case or tank through port 71. The unbalancedforce of pressure in chamber 59 compresses spring 69 moving spool 56 ofmode shuttle 26 to the position shown in FIG. 1. In this position land61 closes port 76, and land 63 blocks communication between groove 72and bore chamber 58 but permits communication between groove 72 andspool groove 65. Groove 73 provides a bypass around land 62 betweengrooves 64 and 65. Pressure of fluid in groove 73 is applied throughgroove 64 and line 120 into the chamber 119 which is above spool 83. Thepressure of fluid in groove 73 is also applied through groove 65 togroove 72 and through line 115 into bore 114 where it acts on the upperend area of the bypass piston 84.

It is the pressure in the chamber 59 or 59a associated with theparticular mode shuttle under consideration which determines theposition of that shuttle. When that pressure is high (for example equalto the pressure in line 89 or 89a), the spring 69 or 690 is compressedand the mode shuttle is displaced to a position that ports the flowlimiter-check valve component 27 or 27a so that it acts as a flowlimiter. Alternately, when the pressure in chamber 59 or 59a is low, thespring expands and the mode shuttle is displaced to that position (theposition of the mode shuttle 26a in FIG. 1) that ports the flowlimiter-check valve component to act as a check valve. It should benoted that it is possible to change the porting so that pressures of theopposite sense control the mode shuttle. For example, the pressure ofthe stroking piston can be used to control mode shuttle 26 within theconcept of the invention.

With variable unit 10 operating as a motor, inlet flow in bore 82 passesthrough orifice 87 in spool 83, causing a reduced pressure in thevicinity of holes 93. This reduced pressure is transmitted throughgroove 92 to port 95 and through line 96. to groove 73 of the modeshuttle 26, from groove 73 through line 120 to primary control chamber119 in bore 82 where it exerts a downward or valve opening force onspool 83. Pressure from groove 73 is also transmitted through line intothe secondary control chamber formed by bores 114 and 102, and actsdownwardly on the upper surface of the bypass piston 84. The total areaabove spool 83 thus sees the reduced pressure downstream of restrictor87 (under these circumstances the bypass piston and associated portingcan be ignored).

The ports 98 in spool 83 cooperate with groove 99 to define a throttlingvalve or orifice which regulates the flow of inlet fluid from bore 82 tomotor inlet line 16. The valve 98, 99 is shown in full open position inFIG. 1, and it progressively closes by upward movement of spool 83, seeFIG. 3. As inlet flow increases, the pressure drop across orifice 87increases, and the pressure in line 96 is reduced. Since the pressure inline 96 is directed or ported by mode shuttle 26 to exert a downward orvalve opening force on spool 83, that force is also reduced. The size ofthe opening of the flow limiting valve 98, 99 is determined by thebalance of the pressure forces acting upwardly on spool 83, and thecombined pressure force and spring force acting downwardly on the spool.When the flow to the motor increases to a level such that the pressurein line 96 is sufficiently low that the upward valve closing pressureforce exceeds the combined preload on spring 85 and pressure force inprimary chamber 119 that tend to hold the flow limiter open, the spool83 moves upward and starts to close, and tends to limit the flow to themotor.

One characteristic of a flow limiting valve which must work over a largepressure range, is that the flow forces tending to make the valve closebecome very large as the valve closes. if these forces become too great,the valve can go unstable and either suddenly shut or oscillate. If theload, i.e., the mass of the rotating groups, has appreciable inertia, asit may have with the pump and motor shown here, instability of a flowlimiting valve can be oscillatory and can result in cycling of flow,that is, cyclical flow variations with successive peaks and minimas. Themechanism is one wherein high flow causes the valve to move towardclosing; the inertia of the rotating groups keeps the flow nearlyconstant during this part of the cycle, rather than letting it diminishas it would in the absence of the inertia. Thus the closing flow forceincreases very rapidly, and if the rate of increase is great enough, cancause the valve to slam shut. The rotating groups ultimately slow downso that the flow in the motor inlet 16 reduces, the valve closing forcedecreases, and the flow limiter valve reopens whereupon the flow cyclestarts again.

To avoid this type of instability, l have provided the angulated bores100 which are in parallel with the main throttling ports 98. Theseorifices 100 provide an opening flow force that bucks the closing flowforce, and l have found that their provision assists greatly instabilizing the operation of the valve. As shown by the ar- I rows inFlG. 3, flow through diagonal bores 100 to groove 99 is generallyupward, and it exerts a reaction force on the spool which is opposite tothe upward reaction force of the angularly downward flow of fluid fromports 98 to groove 99. These flow forces tend to cancel; without thebores 100 the full valve closing reaction force from flow through ports98 would exert a larger closing force on spool 83, with poorer valvestability.

With respect to the other flow limiter-check valve 27a, it acts as acheck valve with a variable bypass to tank. It directs to bore 82a thatquantity of fluid which is demanded by the B system and it bypasses totank the remainder of the pump output volume from line 19. Mode shuttle26a directs operation of the flow limiter-check valve 27a as a variablebypass check valve. The mode shuttle vents the secondary chamber 114a atthe upper end of the bypass piston 840, through line 1 a, groove 72a,and chamber 58a.

' The flow limiter-check valve 27a is shown in FIG. 1 in the position itoccupies when the entire pump output flow is being directed to tank andnone to bore portion 82a-that is, when the work load demands no flow. in

. these circumstances, pressure beneath spool 83a is high. The secondarychamber formed by bores 114a and 102a is vented to tank via mode shuttle56a, so that anet upward pressure force is exerted on spool 83a andpiston 84a. This net pressure force moves spool 83a upwardly,compressing spring 850 and moving piston 84a upwardly to the positionshown. Spool 83a abuts insert 1034 at a position at which the valve 98a,99ais closed, and pressure fluid does not flow to bore 86a from thepump. Piston 84a is held in the position shown such that fluid from line19 is released totank via line 1 17a, groove ll8a,'diagonal bore 116a,groove 106a, slots 107a, bore 114a, line 115a, chambers 58a, and port71a. The pressure of fluid in line 19 is applied into chamber 1190, butbecause chamber 114a is vented, this pressure acts downwardly on spool83a over a smaller net area than the area on which pressure beneath thepiston acts. Valve 98a, 99a remains closed until the pressure in line 19exceeds the pressure in bore 82a by some value determined by the area ofspool 84a, the area of spool 83a, and the force of spring 85a; thisindicates a demand for flow to the B system. The downwardly acting forceon spool 83a then begins to exceed the upwardly acting force. Withdownward From this description, it can be seen that spool 83a acts as acheck valve, opening to permit flow fromline 19 to bore 82a only whenthe pressure in line 19 is greater by some value than that in bore 820.Thus the same structure which acts as a flow limiter for the motor, isported differently to act as a check valve for the pump.

While the variable bypass structure shown is preferred, it is not anecessary part of this fluid transfer package. It may be omitted, andpistons 84, 84a for example can be replaced by solid pistons and theassociated porting for carrying the variable bypass flow can beeliminated.

In the foregoing description the transfer package has been described asincluding a variable unit and a fixed unit. The unit 10 however need notin principle be a variable unit, and the reversibility of controlfeatures provided by this invention may be utilized with to fixed units.f

Having described my invention, I claim:

1. ln fluid power transfer apparatus including interconnected first andsecond fluid pressure translating devices,

the improvement comprising,

valve means including a flow limiter and a check valve for each device,said flow limiter increasingly restricting the rate of flow through itas the flow increases,

and sensing and control means responsive to the demand for transfer ofpower from the first device to the second to interconnect the flowlimiter in series with the. first device and to interconnect the checkvalve to the outlet of the second device,

said sensing and control means also being responsive to the demand fortransfer of powerfrom the second device to the first to interconnect theflow limiter in series with the second device and to interconnect thecheck valve to the outlet of the first device. i

2. The improvement of claim 1 wherein the sensing and control meansincludes a pressure operated shuttle exposed at opposed surfaces thereonto pressures in fluid systems served by the first and second devicesrespectively.

3. The improvement of claim 2 wherein said sensing and control meansalso includes secondary opposed areas on said shuttle,

and means applying the higher of the pressures in the said systems toone secondary area and venting pressure on an opposed secondary area,and providing a deadband range of system pressures in which said shuttledoes not shift in response to fluctuations in system pressure.

4. The improvement of claim 1 which includes mode reversing means whichreverse the connections of the flow limiter and check valves to therespective devices when the direction of transfer of power is reversed.

5. The improvement of claim 4 wherein the mode reversing means isresponsive to and is'actuated by the sensing and control means.

6. The improvement of claim 1 wherein the flow limiter and check valveassociated with each respective device are combined in a singlecomponent comprising a spool cooperating with a port in a bore to form avalve,

said valve connected at all times in series with the pressure side ofthe respective device.

7. The improvement of claim 6 which includes means applying the pressurein the system served by the respective device to an end surface of saidspool to act thereon in a direction tending to close said valve, aspring biasing said valve open, an opposed surface of said spoolsubjected to a biasing pressure in a primary control chamber which is apressure reflecting the rate of flow -of fluid through said valve whenthe associated device is acting as a motor and which is the pump outletpressure when the associated device is acting as a P p and anothersurface associated with said spool and opposed to said end surface,subjected to a pressure in a secondary control chamber which pressure isequal to the pressure in the primary control chamber when the associateddevice is acting as a motor and which is vented when the associateddevice is acting as a pump.

8. The improvement of claim 1 wherein the flow limiter and check valvefor each device are a single double function valve comprising a borehaving a port communicating with the pressure side of the respectivefluid pressure translating device,

a movable valve element forming a variable orifice with said port,

an end area of said element exposed in use to pressure in the systemserved by the respective device, said pressure urging the element in adirection tending to close said variable orifice,

spring means biasing said variable orifice open,

a flow restrictor establishing a pressure drop in response to flowbetween the pressure translating device and the respective system,

a first control chamber including a surface of said valve elementopposite to said end area, pressure in said chamber tending to open saidvariable orifice,

a second control chamber including another surface associated with saidvalve element opposite to said end area,

and means for establishing different pressures in said first and secondcontrol chambers to operate said double function valve as a check valveand as a flow limiter.

9. The improvement of claim 8 including,

means responsive to the operation of the respective fluid pressuretranslating device as a motor to apply the pressure on the lowerpressure side of said flow restrictor to said first and second controlchambers and operate said double function valve as a flow limiter, andresponsive to the operation of the respective fluid pressure translatingdevice as a pump to apply the pressure developed by said pump to saidfirst control chamber and to vent said second control chamber to operatethe double function valve as a check valve.

10. The improvement of claim 9 wherein said flow restrictor is providedin said movable element in the flow path between said end area and saidport.

11. The improvement of claim 10 wherein said movable element is a spo olhaving an internal cavity therein with an opening m a sidewall thereofwhlc forms said variable orifice with said port, and communicating at anend area thereof with said flow restrictor.

1. In fluid power transfer apparatus including interconnected first andsecond fluid pressure translating devices, the improvement comprising,valve means including a flow limiter and a check valve for each device,said flow limiter increasingly restricting the rate of flow through itas the flow increases, and sensing and control means responsive to thedemand for transfer of power from the first device to the second tointerconnect the flow limiter in series with the first device and tointerconnect the check valve to the outlet of the second device, saidsensing and control means also being responsive to the demand fortransfer of power from the second device to the first to interconnectthe flow limiter in series with the second device and to interconnectthe check valve to the outlet of the first device.
 2. The improvement ofclaim 1 wherein the sensing and control means includes a pressureoperated shuttle exposed at opposed surfaces thereon to pressures influid systems served by the first and second devices respectively. 3.The improvement of claim 2 wherein said sensing and control means alsoincludes secondary opposed areas on said shuttle, and means applying thehigher of the pressures in the said systems to one secondary area andventing pressure on an opposed secondary area, and providing a deadbandrange of system pressures in which said shuttle does not shift inresponse to fluctuations in system pressure.
 4. The improvement of claim1 which includes mode reversing means which reverse the connections ofthe flow limiter and check valves to the respective devices when thedirection of transfer of power is reversed.
 5. The improvement of claim4 wherein the mode reversing means is responsive to and is actuated bythe sensing and control means.
 6. The improvement of claim 1 wherein theflow limiter and check valve associated with each respective device arecombined in a single component comprising a spool cooperating with aport in a bore to form a valve, said valve connected at all times inseries with the pressure side of the respective device.
 7. Theimprovement of claim 6 which includes means applying the pressure in thesystem served by the respective device to an end surface of said spoolto act thereon in a direction tending to close said valve, a springbiasing said valve open, an opposed surface of said spool subjected to abiasing pressure in a primary control chamber which is a pressurereflecting the rate of flow of fluid through said valve when theassociated device is acting as a motor and which is the pump outletpressure when the associated device is acting as a pump, and anothersurface associated with said spool and opposed to said end surface,subjected to a pressure in a secondary control chamber which pressure isequal to the pressure in the primary control chamber when the associateddevice is acting as a motor and which is vented when the associateddevice is acting as a pump.
 8. The improvement of claim 1 wherein theflow limiter and check valve for each device are a single doublefunction valve comprising a bore having a port communicating with thepressure side of the respective fluid pressure translating device, amovable valve element forming a variable orifice with said port, an endarea of said element exposed in use to pressure in the system served bythe respective device, said pressure urging the element in a directiontending to close said variable orifice, spring means biasing saidvariable orifice open, a flow restrictor establishing a pressure drop inresponse to flow between the pressure translating device and therespective system, a first control chamber including a surface of saidvalve element opposite to said end aRea, pressure in said chambertending to open said variable orifice, a second control chamberincluding another surface associated with said valve element opposite tosaid end area, and means for establishing different pressures in saidfirst and second control chambers to operate said double function valveas a check valve and as a flow limiter.
 9. The improvement of claim 8including, means responsive to the operation of the respective fluidpressure translating device as a motor to apply the pressure on thelower pressure side of said flow restrictor to said first and secondcontrol chambers and operate said double function valve as a flowlimiter, and responsive to the operation of the respective fluidpressure translating device as a pump to apply the pressure developed bysaid pump to said first control chamber and to vent said second controlchamber to operate the double function valve as a check valve.
 10. Theimprovement of claim 9 wherein said flow restrictor is provided in saidmovable element in the flow path between said end area and said port.11. The improvement of claim 10 wherein said movable element is a spoolhaving an internal cavity therein with an opening in a sidewall thereofwhich forms said variable orifice with said port, and communicating atan end area thereof with said flow restrictor.